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CONTENTS
Volume 34, Number 5, November 2024
 

Abstract
Metaconcrete is a relatively new concept of concrete where traditional aggregates are partially replaced by resonant aggregates which consist of solid core coated with a relatively soft material. In this research, a mass-spring-mass analytical simplified model is used to predict the bandgap characteristics of metaconcrete firstly, then the bandgap characteristics of metaconcrete unit cell are numerically investigated by using finite element software COMSOL Multiphysics, the numerical model is built and verified by the analytical solution in terms of predicting bandgap frequency region. The effect of the parameters such as the modulus of coating, the density and radius of heavy core and resonant aggregate volume fraction on the characteristics of bandgap are studied based on validated finite element model. The vibration attenuation property of metaconcrete slab is studied by using the finite element code LS-DYNA and the effect of the parameters such as the modulus of coating, the density and radius of heavy core and resonant aggregate volume fraction. Metaconcrete slab exhibit prominent vibration attenuation capacity in the predicted bandgap. Finally, a frequency sweeping experiment is carried out to verify the theoretical model. The experimental results show that metaconcrete specimens exhibit excellent vibration attenuation ability in the predicting bandgap. The results can be used for designing engineered aggregates for better structural protection.

Key Words
bandgap characteristics; displacement attenuation; experimental verification; local resonance; metaconcrete; stress attenuation

Address
College of Civil Engineering, Taiyuan University of Technology, Taiyuan, Peoples R China

Abstract
Slump is an important index for concrete fluidity, which has a direct guiding effect on construction. In recent years, using RGB images for evaluating slump has been confirmed by scholars. Based on previous studies, this paper investigates the superiority of RGB-D image data over RGB image data in predicting slump of concrete and proposes three RGB-D fusion models: The early-stage-fusion model performs feature fusion in the data input stage, while the fully-connected-layer-fusion model performs feature fusion in the classification layer and the middle-stage-fusion model performs feature fusion after each residual block. In the classification of slump 120 mm, 150 mm and 200 mm, the Precision, Recall and F1-score are used to evaluate the model's ability to classify a single class, and the Accuracy, Macro-F1, Kappa and MCC are used to evaluate the model's performance. The experimental results showed that compared with the model using only RGB images, the fusion model achieve better performance, indicating that RGB-D image data can better evaluate concrete slump.

Key Words
concrete; convolutional neural network; feature fusion; RGB-D images; slump prediction

Address
College of Mechanical Engineering and Automation, Huaqiao University, Xiamen 361021, Fujian, China

Abstract
Concrete structures may be subjected to repair or local dismantling due to changes in the activity or in case of their damage. Current demolition techniques, besides the required time frame for the renewal, involve remarkable affections due to noise, vibration and dust. This research presents a method to carry out such procedures selectively and efficiently, avoiding noticeable affections on the environment and other users. In addition, it could ease the segregation of the construction materials for better recycling. The study analyses the influence of the position and diameter of the reinforcement, the frequency of the applied magnetic field, the thermal conductivity and the specific heat capacity of the surrounding cementitious matrix and the convection and radiation phenomena on the induction heating process. Depending on the setup, high temperatures (above 700 oC) can be achieved in less than 90 s. However, the frequency and the reinforcement position are the most influential parameters, showing a heating rate up to a 300% faster when increasing the frequency 4 times (from 12 kHz to 48 kHz) and a difference up to 250% in the maximum temperature achieved between rebars aligned and misaligned with the magnetic field. A regression analysis performed on the data obtained provides a prediction model that properly fits (R2=0.979) the expected heating according to the variable parameters. Finally, a real scale column case is simulated and observed that closed stirrups can increase the heating above 1000 oC in just 60 s and induce cracking of the matrix.

Key Words
concrete cracking; concrete reinforcement; Joule effect; magnetic permeability; temperature

Address
Aimar Orbe: Construction Engineering Area, Department of Mechanical Engineering, Engineering Faculty of Bilbao, University of the Basque Country (UPV/EHU), Plaza Ingeniero Torres Quevedo 1, 48013, Bilbao, Spain
Roque Borinaga-Treviño and Olatz Oyarzabal: Mechanics of Continuous Media and Theory of Structures Area, Department of Mechanical Engineering, Engineering Faculty of Bilbao, University of the Basque Country (UPV/EHU), Plaza Ingeniero Torres Quevedo 1, 48013, Bilbao, Spain
Ignacio Crespo: Industry and Transport Department, TECNALIA Research & Innovation, Basque Research and Technology Alliance (BRTA), Paseo Mikeletegi 2, 20009, Donostia-San Sebastian, Spain

Abstract
This study developed a novel pipe roofing structure, called secant pipe roofing structure (SPRS), which is widely used in the support field of underground stations. Its flexural studies are essential since the structure is subject to bending load conditions. However, the influence of parameters and methods for predicting ultimate load capacity still needs more attention. Therefore, this study comprehensively investigated the flexural performance of SPRSs via experimental and numerical methods. A total of four SPRS specimens were prepared and tested under in-plane bending. The test results show that all specimens exhibited remarkable ductility. The load vs. displacement curves of SPRSs during the whole testing process were discussed in detail. Besides, numerical simulation of the flexural performance of SPRSs was carried out and an extensive parameter analysis was also made to ascertain the influences of several key variables. Finally, the support vector machine (SVM) and back propagation (BP) models were introduced to predict the ultimate capacity of SPRS. The accuracy and reliability of the developed models were examined according to the available experimental observations and simulated results by finite element (FE) analysis. This investigation provides a valuable reference for the design and application of SPRS in underground stations support.

Key Words
back propagation (BP); finite element; flexural behavior; secant pipe roofing structure (SPRS); support vector machine (SVM)

Address
Bo Lu and Wen Zhao: School of Resources and Civil Engineering, Northeastern University, Shenyang, 110819, China
Wentao Wang: Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, MI 48105, USA
Weiwei Li: Guangzhou Metro Design and Research Institute Co., Ltd., Guangzhou, 510010, China
Pengjiao Jia: School of Rail Transportation, Soochow University, Suzhou, 215131, China

Abstract
This research is a study in which many different parameters are considered together in order to better understand the strength and durability properties of lightweight geopolymer concrete (LWGPC). Volcanic pumice aggregate, which has an important place in the production of lightweight concrete, has been replaced by coarse aggregate at the rates of 25%, 50% and 75%. Second, glass fiber was added as a fraction of volume by weight at 0.5%, 1%, 2%, and 3%. The lengths of the glass fibers of 3, 6 and 12 mm were used. Other variable is the change of NaOH molarity. In addition to the most commonly used 12M, 11M and 13M were also tested in the research. As a result of the experiments, approximately 27 MPa compressive strength and 14 MPa flexural strength were obtained with the addition of 25% pumice aggregate. While 1% and 2% glass fiber additives exhibited good compressive and flexural performance, in the NaOH molarity effect test, the highest compressive strength was obtained with 12M, while the highest flexural strength was obtained with 13M. Concentrations of 12 and 13M did not cause any problems in terms of precipitation, workability and setting time, but the best results were obtained with M12. Using molarity of 11M should be avoided. This study, in addition to making significant contributions to the environmental impact of LWGPC concrete, shows that using 25% pumice compressive strength over 25 MPa can be obtained.

Key Words
compressive; concrete; flexural; geopolymer; glass fibers; recycling; setting; workability

Address
Ali İhsan Çelik: Department of Construction, Tomarza Mustafa Akincioglu Vocational School, Kayseri University, Kayseri, 38940, Turkey
Yasin Onuralp Özkiliç: 1) Department of Civil Engineering, Faculty of Engineering, Necmettin Erbakan University, Konya, Turkey, 2) Department of Technical Sciences, Western Caspian University, Baku 1001, Azerbaijan

Abstract
Two novel laminate constitutive equations (LCE) for the static analysis of anisotropic shells are presented and implemented in this work. The LCE, developed for both two-dimensional (2D) and three-dimensional (3D) analysis, are more general than those obtained using the Kirchhoff-Love (K-L) equations, Reissner-Minddlin (R-M) type models, refined 2D/3D models, and some general anisotropic doubly-curved shell theories. Our study presents a 2D LCE model that accounts for classical mechanical couplings based on previous models plus additional couplings including extensional-twisting-shearing, extensional-twisting, Gauss bending-twisting-shearing, and Gauss bending-shearing mechanical couplings related to the third fundamental, or Gauss tensor. Moreover, the developed 3D LCE model accounts for all 2D mechanical couplings cited above plus additional mechanical couplings due to the section warping tensor, which arises from the stretching-through-the-thickness variable. These mechanical couplings are pertinent to the optimal design of a composite and are often disregarded in various static and dynamic analysis studies. Neglecting these new mechanical couplings in the design and analysis of laminated composite shells (LCS) can result in significant errors, from both physical and mechanical viewpoint. As such, we recommend employing new complete constitutive relations that integrate these pertinent mechanical couplings for the aforementioned study. Based on our analysis of the impact of additional couplings, we have developed several mathematical formulations that address several challenges encountered in laminated shell theory. As we increase the shell's thickness ratio, our research examines the effects of these couplings on mechanical behavior, buckling shape, critical buckling pressure, and failure analysis through computational modelling and various tests. The examination of the thickness ratio of composite shells illustrates the contrast between our newly developed LCE and some existing LCE as the shells increase in thickness.

Key Words
analyze of LCS; computational solutions; general constitutive equations; laminated composite shells; mechanical couplings; optimum design

Address
Mbangue Nzengwa Ekmon, Ngatcha Ndengna Arno Roland, Ngouanom Gnidakouong Joel Renaud and Nzengwa Robert: 1) Laboratory of Energy Modeling, Materials and Methods, University of Douala, P.O.BOX 2107, Douala, Cameroon, 2) Department of Maritime and Port Engineering, National Higher Polytechnic School of Douala, University of Douala, P.O.BOX 2107, Douala, Cameroon
Nkongho Anyi Joseph: 1) Laboratory of Energy Modeling, Materials and Methods, University of Douala, P.O.BOX 2107, Douala, Cameroon, 2) Department of Maritime and Port Engineering, National Higher Polytechnic School of Douala, University of Douala, P.O.BOX 2107, Douala, Cameroon, 3) Department of Mechanical Engineering, Higher Technical Teachers Training College of the University of Buea in Kumba, P.O. Box 249 Buea Road, Kumba, Cameroon, 4) Department of Mechanical Engineering, National Advanced School Polytechnics of the University of Yaounde I – Cameroon, P.O. Box 8390 Yaounde, Cameroon

Abstract
Concrete shear walls have a wide range of applications as one of the primary lateral load-bearing elements in the construction industry. Implementation constraints often lead to the use of lap-spliced Rebar for these walls. The presence of lap-splice allows for longitudinal reinforcement slippage in the lap-spliced region, which, if it occurs, can result in reduced ductility and undesirable seismic performance of the wall. To further investigate this matter, 32 wall models with variations in longitudinal reinforcement diameter, lap-splice length, percentage of transverse reinforcement, and debonded rebar were numerically and analytically studied using finite element analysis. The selected models were subjected to gravity and cyclic lateral loads, considering bond strength and slippage in the lap-spliced region. By comparing the obtained results, including hysteresis curves, ductility, energy dissipation, reinforcement strain, and crack propagation, with continues rebars wall, it was demonstrated that the presence of lap-spliced Rebar for longitudinal reinforcement causes slippage in the lap-spliced region and reduces the structural ductility. Additionally, the results showed that in walls with lap-spliced Rebar, the use of debonding method compensates for the weakness caused by reinforcement slippage, leading to the restoration of ductility and improvement in seismic performance of the wall while ensuring resistance.

Key Words
concrete shear wall; confinement; lap-splice; reinforcement slippage; seismic behavior

Address
Jalal Hasankhani, Reza Sojoudizadeh and Seyed J. Ghaderi: Department of Civil Engineering, Mahabad Branch, Islamic Azad University, Mahabad, Iran
Erfan Shafei: Faculty of Civil Engineering, Urmia University of Technology, Urmia, Iran

Abstract
A new finite element model is formulated and implemented in this analysis to assess the free vibration and elastic stability behaviors of functionally graded carbon nanotube-reinforced (FG-CNTRC) nanocomposite beams. The developed model is founded on an efficient Quasi-3D shear deformation beam theory. The traction-free boundary conditions are guaranteed with no shear correction factors by integrating the hyperbolic warping function for transverse shear deformation and stress through the thickness coordinate. The suggested two-node beam element has four degrees of freedom per node, and the discrete model maintains inter-element continuity by using both C1 and C0 continuities for the kinematics variables. As a result, the isoparametric coordinate system is used to produce the elementary stiffness, geometric, and mass matrices to improve the current formulation. The weak form of the variational principle is used to generate the governing equations. Following the distribution patterns and CNT volume fraction, the mechanical characteristics of used FG-CNTRC beams change gradually over the beam thickness. The high performance of the present beam element is demonstrated by comparing current results to those predicted by previous theories and solution procedures. In addition, detailed numerical research is conducted to investigate the effects of boundary conditions, distribution patterns, and slenderness ratio on the free vibration and buckling responses of FGCNTRC beams. An appropriate reinforcement technique based on optimum distribution patterns can significantly improve computational efficiencies. The developed finite element beam model is computationally efficient and can be explored as a helpful design and optimization tool for CNT-reinforced nanocomposite structures.

Key Words
carbon nanotube reinforcement; distribution patterns; elastic stability; free vibration; Quasi-3D finite element model

Address
Zakaria Belabed: 1) Department of Technology, Institute of Science and Technology, Naama University Center, BP 66, 45000 Naama, Algeria, 2) Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria
Abdelmoumen Anis Bousahla: Laboratoire de Modélisation et Simulation Multi-échelle, Université de Sidi Bel Abbés, Algeria
Abdelouahed Tounsi: 1) Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria, 2) Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran, Eastern Province, Saudi Arabia

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